1. Field of the Invention
The present invention relates to a semiconductor device including an oxide semiconductor and a manufacturing method thereof.
2. Description of the Related Art
There are a variety of kinds of metal oxides intended for many uses. Indium oxide is a well-known material and is used as a transparent electrode material necessary for a liquid crystal display or the like.
Some metal oxides have semiconductor characteristics. For example, metal oxides having semiconductor characteristics include tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like, and thin film transistors in which a channel formation region is formed using such a metal oxide having semiconductor characteristics are already known (see Patent Documents 1 to 4, Non-Patent Document 1).
Examples of metal oxides include not only an oxide of a single metal element but also an oxide of a plurality of metal elements. For example, InGaO3(ZnO)m (m: natural number) having a homologous series is known as an oxide semiconductor of a plurality of metal elements, including In, Ga, and Zn (see Non-Patent Documents 2 to 4).
Further, it is proved that the oxide semiconductor formed using an In—Ga—Zn based oxide as described above can be used for a channel layer of a thin film transistor (see Patent Document 5, Non-Patent Documents 5 and 6).